1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method and device for transmitting an interworking signal (IWS) in a wireless communication system.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16e standard was adopted in 2007 as a sixth standard for international mobile telecommunication (IMT)-2000 in the name of ‘WMAN-OFDMA TDD’ by the ITU-radio communication sector (ITU-R) which is one of sectors of the international telecommunication union (ITU). An IMT-advanced system has been prepared by the ITU-R as a next generation (i.e., 4th generation) mobile communication standard following the IMT-2000. It was determined by the IEEE 802.16 working group (WG) to conduct the 802.16m project for the purpose of creating an amendment standard of the existing IEEE 802.16e as a standard for the IMT-advanced system. As can be seen in the purpose above, the 802.16m standard has two aspects, that is, continuity from the past (i.e., the amendment of the existing 802.16e standard) and continuity to the future (i.e., the standard for the next generation IMT-advanced system). Therefore, the 802.16m standard needs to satisfy all requirements for the IMT-advanced system while maintaining compatibility with a mobile WiMAX system conforming to the 802.16e standard.
Effective transmission/reception methods and utilizations have been proposed for a broadband wireless communication system to maximize efficiency of radio resources. An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference (ISI) with a low complexity is taken into consideration as one of next generation wireless communication systems. In the OFDM, a serially input data symbol is converted into N parallel data symbols, and is then transmitted by being carried on each of separated N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, and an interval of a transmitted symbol is increased, thereby minimizing inter-symbol interference.
Orthogonal frequency division multiple access (OFDMA) is a multi-access scheme in which some of available subcarriers are independently provided to respective users in a system using an OFDM as a modulation scheme, thus realizing multiple accesses. In the OFDMA, frequency resources such as subcarriers are provided to the respective users, and the respective frequency resources do not overlap with one another in general since they are independently provided to the plurality of users. Consequently, the frequency resources are allocated to the respective users in a mutually exclusive manner. In an OFDMA system, frequency diversity for multiple users can be obtained by using frequency selective scheduling, and subcarriers can be allocated variously according to a permutation rule for the subcarriers. In addition, a spatial multiplexing scheme using multiple antennas can be used to increase efficiency of a spatial domain.
The femto base station (BS) technique can be applicable to the 802.16m system, which is recently actively studied. A femto BS refers to a small mobile communication BS used in indoor areas such as homes, offices, and the like. A femto BS is used to have a meaning similar to that of pico-cell, and generally, a femto BS is recognized to have an advanced function compared with a pico-cell. A femto BS, which generally has low transmission power, provides an access to a subscriber group including access providers. The femto BS is connected to an IP network propagating in homes and offices, and accesses a core network (CN) of a mobile communication system through the IP network to provide a mobile communication service. Namely, the femto BS is connected to the CN of the mobile communication system through a broadband connection such as a digital subscriber line (DSL), or the like. Also, the femto BS may communicate with a femto BS-overlaid macro BS by exchanging a control message with each other through air interface. A user of the mobile communication system may be provided with a service in an outdoor area through an existing macro BS and may be provided with a service in an indoor area through the femto BS.
Complementing a degradation of a service of an existing macro BS within a building, the femto BS improves an indoor coverage of a mobile communication system and provides a service only to determined particular users, so the femto BS can provide high quality voice service and data service. Also, the efficiency of a next-generation cellular system using a high frequency band can be enhanced by reducing the size of a cell, and since several cells each having a small size are used, the number of times of reducing frequency can be advantageously increased. In addition, the femto BS can provide a new service which is not provided in the macro BS, and the propagation of the femto BS accelerates a fixed-mobile convergence (FMC) and reduces the industry-based costs.
In general, the femto BS operates within a predetermined frequency band and may use the same frequency band as or a different frequency band from that of the macro BS. Coverage of the femto BS may overlap with that of the macro BS. The femto BS is required to be synchronized with a network by a common timing, frequency, and cell ID, and the femto BS and the macro BS may be discriminated by a cell ID. When the macro BS and the femto BS coexist, a mobile station may check the presence of the femto BS and attempt handover to the femto BS. Here, in order to check the presence of the femto BS, various methods may be proposed.